Building a Porsche 3,0l 944 turbo

Now the details that affect VEMS specs and installation.


Porsche 944 turbo trigger:

I.e. trigger is 132+1

Shopping list

Assembled v3.3 controller



Serial_nr= 748

pump-= 4.16V



pump+= -3.3mV/200 Ohm


(C103=1nF, no D100)

Firmware 1.1.24

This is how I made the version of MegaTune I'm currently using ( got these instructions, I didn't make them up myself ). There was a conflict inMegaTune's files, which caused erratic PW indication. It was solved with this:

I downloaded, unzipped and copied doc\megatune\vemsv3.ini -file. Then I downloaded, unzipped and wrote over MegaTune2.25\mtCfg -folder's vemsv3.ini -file with that previous .ini-file.

This part IS NOT CORRECT, do not use!

''Part of config, I'm running this trigger with div_by_2 with these settings:


















Auditrigger was initially according to PhatBob?'s instructions:

EC36#27 VR+ ( primary ) = CRANK speed sensor

EC36#13 VR+ ( secondary ) = reference sensor (whel HALL!)

EC36#26 VR- ( primary & secondary )

but changed to

EC36#27 VR+ ( primary ), = CRANK speed sensor

EC18#12 VR+ ( secondary ), = VR reference sensor

EC36#26 VR- ( primary )

EC36#26 VR- ( secondary )

after discussions with Miska. So installation instructions should be updated considering this part.

Before connecting VR-sensors, check their polarity. They should be so that positive current arms the sensor and negative current triggers it. Just in the reverse order than in the picture on the bottom of this thread!!







Pictures of my Genboard v3.3, large files, zipped:



Update 16-11-2007

Finally I've managed to get the car idling well, there's been both mechanical and program related problems. Now triggering issues are solved and VEMS is definately suitable also for this kind of installation.

I would like to thak all those who have helped me with my project!!

Next update will arrive as soon as there's something to update...

Issue report 13-12-07

Engine idles well and is tuneable, but stalls when trying to increase rpm. It doesn't matter if you try to open the throttle slowly or rev it. 1600-1800 is the borderline, no rpm higher. Idle limit is exceeded ( 3 vs 7 % ). From links above can be found almost all relevant data, except scoped trigger signal.

Issue report 2007-12-29

Engine idles well and runs too up to 3000+ rpm, thanks to new config made by SamiKorhonen?. There's still Trigger Error flags visible and above 2500rpm severe misfires. Is it trigger config or signal noise related??

'''Are you still running 1.1.24 (or 1.1.27 You could try 1.1.27, although I don't see 132 tooth related changes; the fuel pulsewidth reported to megatune changed so new vemsv3.ini needed for 1.1.27 to get the fuel pulsewidth correct in logs, but the real output pulsewidth NOT effected ) ?

Make sure all the info necessary for IssueReports is available on your page, and uptodate. Otherwise reproducing the setup on bench is not feasible.'''

Yes, 1.1.24 still in use, waiting for 1.1.32. The fuel PW is no longer a problem, it's solved an MegaTune is also working fine. I've addaed mct and mcd files, can be found from link above. Also included pictures of my Genboard, if that helps solving possible harware issues or need for changed bits & pieces...

Issue update 16-01-08

In this file:

you can find my first scoped pictues. Please study them all, data contained is scattered in them. I'm need all advice concerning oscilloscoping, I guess there's lot to do in improving readability of that data. All pictures are taken from cranck'd engine, harness disconnected and osciloscope's sensors connected to appropriate pins. Scope's GND is connected to sensor GND.

BTW, after soldering a bridge to the red area and installing 1.5 kohm pull-down resistor between green dots, severe misfiring starts at 1000 rpm.


And here's one screenshot of scope, which shows inverted reference sensor signal...


So this might be the answer to remaining problems. Check and double check VR-sensors' polarity before installing them!

17-01-08 Update

I checked and switched reference sensor's polarity, and the car runs now without Trigger Error flags. Revs beautifully, no signs of misfires whatsoever!

06-05-08 Update

I have been struggling for long with another major issue after triggering was cured. Symptoms were incorrect PW and duty_cycle values in the MegaTune and grossly rich mixture with inability to lean it under load. In the end it caused mechanical trouble, and now the engine is been taken apart. The solution for this was quite simple, here's a quote from my text on another VEMS forum ( UK ) :

OK, at least the PW -problem is now solved. I changed Vemsv3.ini-files in 1.1.23 Megatune mtcfg for same ones from 1.1.24 and PW @ idle is around 3.0, without any other modifications. It's now easier to start solving remaining questions.

So there were these conflicting files causing all this trouble again, I had forgotten to do this change to my laptop too! Last time I did it was to the computer in my garage, and symptoms started again when I took the car out in the spring. I also got MegaTune running properly with my newer laptop by using a PCMCIA to D-sub -adapter instead of USB-one.

I also took a short run on the road with my car, it pulls, boosts, whizzles and dumps to atm with a certain urge...